Took one of my new builds out to shoot last weekend. Fired the first round fine, but then I'd have to pull the trigger again to "reset" the gun before it would fire again. On the second trigger pull I could hear and feel it reset if that makes sense. Complete upper from PSA, I built the lower with a PSA LPK.

Did you have to manually pull back on charging handle after first shot to re-cock? Or did it fully cycle but on the second trigger pull nothing happens but it reset on the third trigger pull? I assume it cycled and chambered a round like normal after the first shot. If that's the case it sounds like something with the trigger. I've never pulled the trigger on a follow up shot with nothing happening but then feeling it reset with a second pull.

You might run through a functions check with the gun unloaded so you can feel/hear if the hammer is cocking back and not releasing when you manually cycle. Check the safety too while you do the functions check. Make sure it doesn't fire on safe. To be clear, when I say reset I mean after you pull the trigger, hold it fully depressed to the rear. Then manually charge while continuing to hold the trigger back. Then slowly release the trigger and you should hear and feel a metallic click.

If you fire and it feels like it cycles but doesn't pick up the next round out of the mag the first step is trying a new mag because I'm sure you have several. If it's doing that with several mags it may be undergassed and not forcing the bolt fully to the rear, or not far enough for the bolt to eject and pick up the next round.